What subwoofer can i use with my speakers?

My system consists of the following:

Wadia 850- CD player
Audio Research LS7- Pre Amp
Classe CA200- Power Amp
Magnepan 2.7 QR- Speaker
Martin Logan Aerius- Speaker
Note: I switch between the 2 speakers. I'm thinking of just
getting another pair of speakers (pre-owned Thiel CS3.6), instead of getting a subwoofer as I'm fond of the other 2 only sometimes they sound lacking in bass.
There are a number of good subs out today but 2 I can tell you to try from experience are the REL or ACI due to their flexibility in set up. The big RELs (Studio and Stentor) are excellent but expensive, the ACI Titan II LE is very good bang for the buck.
If you like Thiel bass, you might want to consider a Thiel subwoofer.
Martin Logan Depth or the larger Descent. Steve
I own REL Staduim III - Love It!
I'll suggest a Sunfire from my most recent experiences. However you need to listen to Sunfires & REL's with your own ears. Getting opinions and recommendations are very appealing but your ears will know what sound the best with your Maggies. Happy hunting and listening..............
What about Velodynes? They were big 6-8 years ago(r they still?) but no one has said anything about them.
When I was auditioning subwoofers 1-2 years ago, Velodynes were outclassed by the Rels and the Vandersteen that I heard and the ACI Titan II LE that eventually chose.

Also I've read from many Maggie owners who are very pleased with their ACI Titan II or Rel subwoofer.

(BTW, though I've never heard it, it seems that the new ACI Force would be quite competitive with a Rel Strata or Storm.)
I own a new REL Strata III and love it. I have it teamed up with my Totem Model 1's.
Well it looks like the concensus is either REL or ACI.My question now is do you go thru the low level inputs or thru the speaker level inputs? It would seem that going thru the low level inputs will not degrade the sound as much as the other way around. Or not? Comments greatly appreciated.
Many folks seem to prefer speaker level connections, hearing and/or thinking that there is a better match/integration with the main speakers if the subwoofer receives the same signal from the amplifier as the main speakers. I can't say that I've noticed a difference between the high level and speaker-level connections into ACI or REL subwoofers that could not be dealt with by an adjustment of the subwoofer's level control (but all the usual caveats apply).

The ACI offers both connection options, but, due to some peculiarities of my setup, I often detected a low-level hum when I used the speaker level connecters. The hum disappeared when I changed to shielded ICs between my preamp. outputs and the low-level inputs of my Titan II LE.

This low-level connection also allows me to insert, between my preamp. and amp., a pair of ACI's virtually transparent (to me at least) 65 Hz. 12 db./octave high-pass filters which seem to relieve a little congestion in my Vandersteen 1C's bass and lower midrange.

When I run the Vandersteens full-range (unfiltered), I lower the Titan II's crossover points a little - to just a hair above their lowest settings, and the subwoofer fills in the bottom octave Rel-style.

I usually employ the high pass filters, but when there are few high-amplitude bass transients to challenge my 2-way Vandersteens, the Rel method has worked fine.